In song learning, white-crowned sparrows (Zonotrichia leucophrys) begin mem
orizing conspecific song models at around 20 d of age. Even prior to song m
emorization, however, between 10 and 20 d of age, these birds respond diffe
rently to playbacks of conspecific and heterospecific songs. To investigate
the acoustic cues underlying this early song discrimination, we measured t
he vocal responses of newly fledged young to playbacks of modified conspeci
fic and heterospecific songs. Fledgling white-crowned sparrows responded mo
re strongly to songs containing conspecific notes than to songs containing
notes from other species. In contrast, the presence or placement of an intr
oductory whistle, present in all white-crowned sparrow songs, did not affec
t response levels. A whistle has previously been shown to serve as an acous
tic cue for song memorization and production in this species. Such differen
t responses to the species-typical introductory whistle at different stages
suggests that developmental changes occur in the template system underlyin
g song learning, the factors governing song recognition, or both.